Anomalous coloration in European pine marten Martes martes in Elba Island, Central Italy

Abstract Evidence of abnormal coloration in wild animals provides useful information to better understand its adaptive function and its impact on survival. For this reason, we need to know the frequency and distribution of these abnormal phenotypes in wild populations. Here, we report two records of hypopigmentation in European pine marten Martes martes, obtained during a camera‐trapping survey on Elba Island, Central Italy. We do not know what has caused anomalous coloration of pine marten on Elba Island, but it is possible that the inbreeding may have played a role in this isolated population. Although the light coloration certainly entails an increased visibility of pine martens, it is possible that the low predator pressure and the absence of other wild carnivore populations in our study could mitigate the mortality risk due to the light phenotype. The increased use of camera traps across the world can potentially facilitate the discovery of cases of anomalous colorations in wild populations, providing an unprecedented insight into the occurrence of this phenomenon in wild mammal species.

total body discoloration, but rarely is accompanied by hypopigmented eyes (Abreu et al., 2013;Lamoreux et al., 2010;Lucati & López-Baucells, 2017). Dilution is characterized by paler and more silvery coloration than normal due to insufficient pigmentation (Gong et al., 2021;Lamoreux et al., 2010). Abnormal colorations often occur in isolated and genetically homogenous populations as they are caused by single mutations in specific genes (Abreu et al., 2013;Hubbard et al., 2010). However, records of this phenomenon in wild populations are underestimated and often misclassified due to difficulties in capturing specimens and performing genetic testing (Gong et al., 2021).
Here, we report evidence of hypopigmentation in the European pine marten Martes martes, an elusive medium-sized mustelid distributed throughout much of Europe and northern and Central Asia, and inhabiting a variety of habitats (Aubry et al., 2012). In Italy, the species is present with a fragmented distribution in the forested areas of the peninsula, but it has been recently detected even in anthropic and cultivated areas (Balestrieri et al., 2010;Manzo et al., 2018). Insular populations occur in Sardinia, Sicily, and Elba (Genovesi & De Marinis, 2003). The coat color of pine marten ranges from to dark brown to tawny, with a creamy-yellow throat patch and pale fur within ears (Genovesi & De Marinis, 2003; Figure 1). The fur changes seasonally, being longer and lighter in color in winter and becoming shorter and darker in summer ( Figure 1). Geographical, seasonal, and age-related variation in fur color, with a tendency toward partial lightening, have been reported for other representatives of the genus Martes Pinel 1792, such as sable M. zibellina (Safronov & Zakharov, 2014), Japanese marten M. melampus (Funakoshi et al., 2017), M. flavigula (Gong et al., 2021), and stone marten M. foina (Delibes & Amores, 1986;Masseti, 2009). However, anomalous coloration in European pine marten has never been documented in scientific literature.

| MATERIAL S AND ME THODS
As a part of a larger study on European pine marten distribution on Elba island (42°47'12''N, 10°16'28''E), we conducted a cameratrapping survey between February and July 2020. Elba Island is the largest island of the Tuscan Archipelago (Central Italy) with a total area of 223 km 2 . The island is characterized by high geomorphological heterogeneity and by an altitude ranging from sea level up to 1019 m a.s.l. (Monte Capanne), leading to the establishment of three distinct bioclimatic belts and a large vegetation diversity (Foggi et al., 2006).
The climate is Mediterranean with mean yearly temperature of 16.5°C (min. 10°C in January, max. 24.5°C in July) and mean yearly precipitation of 595 mm (min. 13 mm in July, max. 86 mm in November). More than half of the island (127.4 km 2 ) was designated as a National Park in 1996. The pine marten is the only wild carnivore species present on the island; however, the presence of domestic and feral cats on the island does not allow us to consider Elba Island a competitor-free area.
Currently available information about pine marten on Elba Island covers the origin, distribution, feeding habits, and spatiotemporal activity of the species (De Marinis & Masseti, 1993Mori et al., 2021).
We generated 1-km 2 grid cells over the entire island and then we fixed the centroids, which represent the ideal camera locations ( Figure 2). We positioned 77 camera traps (Trophy cam HD Aggressor, No Glow, model 119877, Bushnell Outdoor Products), which remained in the field for 30 days. Camera traps were placed in the field as close as possible to the ideal locations, at sites where a suitable tree, shrub, or rock was available for mounting the camera and where the surrounding area was sufficiently open for the camera to have a clear view. Cameras were placed at 0-30 cm above the ground, unbaited, and set to record 30-s-long videos when triggered, with a 1-min delay. We recorded a total of 365 marten videos in 55 of 77 sampling sites (71%) during a span of 2310 trap-days.

| Results
On March 10, 2020, at 08:22 h UTC+1 and on May 23, 2020, at 08:34 h UTC+1, two videos of pine marten with anomalous coloration were recorded by camera traps located in two different parts of F I G U R E 1 Camera trap images of regularly colored pine martens from the study area, showing the tawny coat with a creamy-yellow throat patch: (a) longer and lighter winter fur; (b) shorter and darker summer fur Subsequent investigation revealed that a pine marten with pale yellow coat had already been seen in the previous months by a local hunter, at the same site where we recorded the aforementioned May video. According to the morphological features (i.e., body shape) of the animals noticeable in the two videos, we could hypothesize that the records concern two different individuals. The distance between the two camera locations (about 9 km, Figure 2) might support this suggestion. Although there are no published studies on pine marten spatial distribution on Mediterranean islands, the distance between the two cameras was larger than the home range size and distance estimated for this species in Central Italy (Bartolommei, Gasperini, et al., 2016;. Both videos show adult pine martens (i.e., individuals older than 1 year) with a lack of pigmentation throughout the whole body including the nose and with black eye color (Figures 3 and 4). Although the hypopigmentation of the nose might suggest albinism (Fertl & Rosel, 2002;Gong et al., 2021), the eye color leads us to suppose that it could correspond to a case of leucism rather than albinism. In fact, the marten fur appears not to be totally depigmented and was pale yellow with an even lighter throat patch in the standard location (Figures 3 and 4).

| DISCUSS ION
Depigmentation has been often studied as a stage of the domestication process (Cieslak et al., 2011;Trut et al., 2009). However, the frequency of these color anomalies could be higher in small and isolated wild populations due to inbreeding or founder effect, which may increase the expression of recessive phenotypes (Abreu et al., 2013;Bensch et al., 2000;Hubbard et al., 2010;van der Geer, 2019). In Central Norway, Hofmeester et al. (2021)  have few predators (Abreu et al., 2013;Hubbard et al., 2010;Peles et al.,1995). Allen et al. (2019)

ACK N OWLED G EM ENTS
We are grateful to the Parco Nazionale dell'Arcipelago Toscano, its directors M. Burlando and F. Giannini, for making this research possible. We thank Andrea Bonacchi for the English revision.

CO N FLI C T O F I NTE R E S T
The authors declare no competing interests.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.